Technical Field
The present invention relates to an electrical discharge machine and a method for manufacturing a machined object using the electrical discharge machine.
Related Art
An ultrasonic motor is conventionally known (refer to, for example, JP-A-2011-104735). The ultrasonic motor is used in an electrical discharge machine to move an electrode holder that holds an electrode. The ultrasonic motor has a fingertip that comes into contact with the electrode holder. The ultrasonic motor drives the electrode holder by moving the fingertip in an annular manner at an ultrasonic-range frequency.
When an ultrasonic motor such as this is used, the movement of the electrode holder can be controlled to be at an extremely short unit of distance (such as 1 μm or less). However, according to experiments conducted by the inventors, problems may occur when a roller bearing is used as a member for guiding the movement of the electrode holder in a driving direction. In the roller bearing, a plurality of rolling elements are interposed between a movement block and a rail.
Specifically, when the electrode holder is moved over a long period at an extremely short unit of distance, slide resistance in the roller bearing increases. The movement speed of the electrode holder decreases. As a result, it is highly likely that the time required for machining will increase.
The reason such a phenomenon occurs is that dust is produced between the rolling elements and the surrounding path. When movement of the electrode holder by an extremely short unit of distance is repeatedly performed numerous times, the plurality of rolling elements within the roller bearing move by minute vibrations, without rotating. As a result, dust is produced by the roller elements and the surrounding path rubbing against each other.